As a related art, there is proposed an inverter apparatus of a voltage type for increasing a motor terminal voltage to thereby increase loss in braking. (refer to, for example, Patent Reference 1)
FIG. 10 is a block diagram of the inverter apparatus of the related art, commercial power source is converted into direct current by a rectifying portion 101, a voltage rectified thereby is smoothed by a capacitor 102 to be applied to an inverter portion 103. At the inverter portion 103, semiconductor elements are successively switched by a signal, mentioned later, to provide alternating current and an output of the alternating current is supplied to drive an alternating current motor 104. Here, the inverter portion 103 is provided with, for example, 6 pieces of transistors 201 through 206 and 6 pieces of diodes 207 through 212 as the semiconductor switching elements. On the other hand, numeral 111 designates a frequency setter, and an output signal Sa thereof is inputted to an acceleration/deceleration limiting circuit 120. The acceleration/deceleration limiting circuit increases the terminal voltage of the alternating current motor 104 by increasing a gain of a voltage control circuit 121 by a first output signal Sb1 applied to the voltage control circuit 121 and a voltage/frequency converting circuit 114, and a second output signal Sb2 applied only to the voltage control circuit 121 and showing that a speed is being operated to reduce. Further, the voltage/frequency converting circuit 114 is an analog/digital converting circuit outputting a pulse Sd having a frequency fd in proportion to a voltage Vb of the input signal Sb1. Further, an output signal Sc of the voltage control circuit 113 and the output pulse fd of the voltage/frequency converting circuit 114 are applied to a modulating circuit 115. The modulating circuit 115 carries out a pulse width modulating control by applying a control pulse to the respective transistors 201 through 206 of the inverter 103 by way of a base drive circuit 116. On the other hand, an output voltage of the inverter 103 is determined by ON/OFF time periods of the respective transistors 201 through 206 controlled by a pulse width of the control pulse, and the pulse width of the control pulse is determined by an output voltage Vc of the voltage control circuit 121. Therefore, the base drive circuit 116 applied with the control pulse from the modulating circuit 115 is controlled to switch by outputting a base voltage and a base current in accordance with a characteristic of the transistors 201 through 206 in correspondence with the control pulse. Further, the alternating current motor can be operated by variable frequency power source by an output of the inverter 103.
An output signal of a setter 118 for setting a predetermined upper limit value of a terminal voltage of the capacitor 102 is applied to a comparator 119 having a hysteresis characteristic to thereby monitor the terminal voltage of the capacitor 102. Further, when the terminal voltage of the capacitor 2 exceeds the predetermined upper limit value in braking, an output signal VCOM is generated from the comparator 119. The acceleration/deceleration limiting circuit 120 follows a set voltage of the frequency setter 111 by a change rate having a predetermined gradient. Further, during a speed reducing operation, an amplification factor of the voltage control circuit 121 is increased. Thereby, the pulse width of the control pulse outputted from the modulating circuit 115 is widened to thereby increase a voltage applied to the alternating current motor 104. It is proposed to increase iron loss and copper loss by increasing the terminal voltage to thereby reduce the speed of the alternating current motor 104 in a short period of time.
Further, as other related art, there is proposed an inverter apparatus of calculating a switching output by a function of always constituting the same output voltage for a direct current voltage detected by a direct current detecting circuit in an operation other than speed reducing and calculating the switching output by a function of a rated direct current voltage value of the alternating current power source in speed reducing operation. (refer to, for example, Patent Reference 2)
FIG. 11 is a block diagram showing an inverter apparatus of the related art. In the drawing, numeral 301 designates a converter circuit constituting a rectifying circuit for converting an alternating current voltage of an alternating current power source 307 into a direct current voltage, numeral 302 designates a smoothing capacitor for smoothing the direct current voltage of the converter circuit 301, numeral 303 designates an inverter circuit constituting an inversely converting circuit for converting a direct current voltage of the smoothing condenser 302 into an alternating current voltage having a predetermined frequency by making a switching element ON/OFF by a predetermined timing, numeral 304 designates a microcomputer for controlling the inverter circuit 303 by a PWM control, numeral 305 designates a base amplifier for outputting a PWM signal for driving a switching element of the inverter circuit 303, numeral 306 designates a direct current voltage detecting circuit for detecting the direct current voltage of the smoothing capacitor 302 and numeral 350 designates the inverter apparatus constituted by the converter circuit 301 through the direct current voltage detecting circuit 306. Numeral 308 designates an induction motor driven by an alternating current voltage of the inverter circuit 303, numeral 400 designates an operation command apparatus for instructing to operate the inverter apparatus 350, the operation command apparatus includes a microcomputer 421, a key sheet 422 and a display 423, and can set operation commands of regular rotation, inverse rotation, stop and an operation command of an output frequency to the inverter apparatus 350. Numeral 314 designates a microcomputer for controlling the inverter circuit 303 by a PWM control and constituted by including a switching output calculating circuit 315 for calculating switching output signals in the operation commands other than speed reducing and in the operation command in speed reducing and RAM 316 for storing the operation commands of regular rotation, inverse rotation, stop and an output frequency set by the operation command apparatus 400. Next, operation of a case of operating an induction motor will be explained in reference to a flowchart in operation of FIG. 12. First, for example, the operation command of regular rotation is inputted by the operation command apparatus 400, next, the operation of output frequency is inputted and operation is started (S11). Next, the microcomputer 421 determines whether stop or not by seeing whether stop flag is on at the microcomputer 421 of the operation command apparatus 400 (step S12). When stop is not determined, the microcomputer 314 reads the operation command of output frequency set to a predetermined frequency (step S13), when stop is determined, the microcomputer 314 reads an output frequency command of 0 Hz (step s14). Thereafter, the microcomputer 314 determines speed reducing or not by seeing whether speed reducing flag is on at the microcomputer 421 of the operation command apparatus 400 (step S15). Further, when speed reducing is not determined, the microcomputer 314 reads the direct current voltage detected by the direct current voltage detecting circuit 306 (step s16), a switching output is calculated by a function constituting a value always set with an output voltage for the direct current voltage, that is, a function of constituting always the same output voltage for the direct current voltage (step S18), the switching output is outputted to the base amplifier 305, the switching element of the inverter circuit 303 is driven by the PWM signal and an alternating current voltage of an output frequency set by the inverter circuit 303 is outputted (step S19). Here, the function constituting the same output voltage for the detected direct current voltage signifies a function of carrying out an operation of correcting the output voltage for a change in the direct current voltage so as not to vary the output voltage for a variation in the direct current voltage. Further, when speed reducing is determined, the direct current voltage value of the smoothing capacitor 302 is constituted by a direct current voltage in a rated alternating current power source voltage, for example, when the rated alternating current power source is 200 V, the direct current voltage value of the smoothing capacitor 302 is constituted by 200×21/2=283 V as the direct current voltage value (step S17), the switching output is calculated by the function (step S18), the switching output is outputted to the base amplifier 305, the switching element of the inverter circuit 303 is driven by the PWM signal and the alternating current voltage is outputted from the inverter circuit 303 (step S19). Thereby, although the output voltage of the inverter circuit 303 in speed reducing becomes the same as the set value when the direct current voltage is constituted by a rated value, when the direct current voltage is increased by the regenerative power of the induction motor 8, the set value is increased in proportion thereto. That is, although in operation not in speed reducing but, for example, in acceleration and constant speed, even when the power source voltage of the alternating current power source 307 is varied, the output voltage of the inverter circuit 303 becomes the predetermined output voltage, in speed reducing operation, even when the direct current voltage is increased by the regenerative power, the switching output signal is calculated by the function of the direct current voltage value as the rated value 283 V which is the value lower than an actual value. As a result, the switching element of the inverter circuit 303 is driven by the direct current voltage value when the alternating current power source 307 is at the rated value regardless of the change in the direct current voltage, and therefore, the output voltage is increased in proportion to an increase in the direct current voltage. Here, the function of the direct current voltage value when the alternating current power source 307 is at the rated value signifies a function in which switching in the rated input voltage of the alternating current power source 307 is carried out even when the direct current voltage is varied and operation of correcting the output voltage is prevented from being carried out. In this way, by increasing the output voltage of the inverter circuit 303 in speed reducing, an exciting current to the induction motor 308 is increased, loss at wirings of the induction motor 308 is increased. This means that after all, the regenerative power of the inverter circuit 303 is consumed by the induction motor 308 by increasing the exciting current to the induction motor 308, the regenerative power to the inverter circuit 303 is reduced in comparison with that in the related art, also an increase in the direct current voltage is reduced. Therefore, a speed reducing function can be promoted without interrupting speed reducing operation and without being accompanied by a circuit of consuming the regenerative power by a resistor or the like. Further, it is proposed to also increase a speed reducing torque by increasing the exciting current.
Patent Reference 1: JP-A-58-165695
Patent Reference 2: JP-A-5-219771